Throughout most of history mankind has handled its solid wastes, particularly municipal wastes or garbage, by burying it or dumping it into bodies of water, but in the face of relatively recent recognition that improper handling of solid wastes can create short term and long term pollution problems, solid waste management has become a matter of increasing concern. Recovery of useable resources from solid wastes is another factor which has lead to increasing concern for proper management and utilization of solid wastes. Of the different types of solid waste, municipal solid waste is the most significant in terms of sheer volume and variety of composition.
Numerous approaches have been suggested and utilized for the handling of solid wastes, though disposal in landfills has been and continues to be the most widely used approach by far. Although disposal in properly constructed, operated and maintained landfills appears to be a relatively safe method of waste management over a short span of time, major concerns remain about the long term safety of even the best designed and operated landfills. Conventional landfills are constructed with a generally impervious liner to serve as a barrier against leaching of wastes into water supplies, but any breach in the liner results in failure of the entire containment system. Further, conventional design and operation of landfills for disposal of solid wastes fails to effectively address the potential for reuse of waste stream components as resources.
Incineration of is another approach which has been in long term use for disposal of solid wastes, sometimes alone and sometimes with recovery of energy from the heat of combustion. Again, while offering partial solutions and recovering at least some portion of the resource value of the incinerated wastes, incineration can produce air pollution, and the use of all waste components for heat is often an extremely inefficient approach to recovery of the resource value of many waste components.
Composting of municipal wastes is another approach which has been attempted, but which has failed to provide a comprehensive solution to the waste management problem. Although some components of municipal waste can be effectively composted, many components are not amenable to biological degradation or may retain toxic or hazardous characteristics through the composting process.
Source separation recycling, in which recyclable and/or reusable materials are separated from the waste stream by each waste generator and separately collected, has been strongly proposed as an effective and efficient solution to solid waste management problems. Source separation recycling, while effective in separating components from the waste stream in order to use their resource value, has met with a number of difficulties.
In the particular case of municipal wastes, source separation of wastes must be done by each waste generating household, and the willingness of the waste generators to participate in detailed separation programs is often a significant determining factor in the effectiveness of the separation, or recycling program. In even the most effective voluntary recycling programs, participation by household waste generators in source separation of wastes at all is not universal, and participation tends to drop as the complexity of separation increases. Problems also arise from errors made by municipal waste generators in identifying materials, resulting in commingling of recovered materials and reduction in the efficiency of separation. In response to the commingling problem, and often in an effort to increase participation, some recycling programs have provided for a combination of source separation and collection separation approaches. In the combined programs reusable materials are separated from other wastes and initially commingled, with additional separation performed as the wastes are collected from each generator. However, combined programs tend to slow waste collection and often require additional manpower, and any improvement in efficiency has been marginal at best.
Another approach that has been used in municipal recycling programs, either alone or in conjunction with separation by each waste generator, is post-collection separation, in which at least some part of the separation process is carried out after collection of wastes from individual households. Post-collection separation techniques range from simple and incomplete manual separation, based upon visual inspection of the waste stream and identification of recyclable materials, to more complex automatic systems utilizing techniques such as magnetic separation of ferrous metals, induction current separation of non-ferrous metals, and density separation in, e.g. water tanks. The effectiveness and efficiency of such separation techniques varies widely, and has proved to be only partially successful as an overall approach. The use of relatively large quantities of water in many conventional separation approaches also creates an environmental water pollution problem while attempting to solve a solid waste problem.
Conventional recycling and reuse approaches have also been plagued with economic problems, and recovered or recycled materials have often proved to be more costly than virgin materials due, at least in part, to inefficient handling, transportation of materials between fragmented processing and utilization facilities, the high cost of the final steps in material purification, and channeling of recovered materials into uses in which they must directly compete with virgin materials. For example, it is commonly perceived that the best recycling use of recovered materials is to return those materials to their original use, for production of the same products from which they were recovered in the waste stream, and while such full loop recycling may be the ideal approach, so long as the commercial economy provides virgin materials at lower cost the utilization of recovered material is suppressed and waste management problems remain unresolved.
There remains a need for an effective method of managing solid wastes, and particularly municipal solid wastes of both domestic and commercial character, so as to directly address and avoid the problems and difficulties of the prior art. There further remains a need for an efficient and cost-effective approach to utilization of recovered materials that coordinates the goal of maximizing recovery and reuse of waste materials with the need to channel those materials into uses that avoid or eliminate the suppressive effect of disadvantageous economic competition with virgin materials.